1. Field of the Invention
The invention relates to a system and a method for providing hearing assistance to at least one user, wherein audio signals from an audio signal source, such as a microphone for capturing a speaker's voice, are transmitted via a wireless link to a receiver unit acting as an audio receiver for an ear-worn device, such as a hearing aid.
2. Description of Related Art
Presently, in such systems, the wireless audio link usually is an FM (frequency modulation) radio link. According to a typical application of such wireless audio systems, the receiver unit is connected to or integrated into a hearing instrument, such as a hearing aid, with the transmitted audio signals being mixed with audio signals captured by the microphone of the hearing instrument prior to being reproduced by the output transducer of the hearing instrument. The benefit of such systems is that the microphone of the hearing instrument can be supplemented or replaced by a remote microphone which produces audio signals which are transmitted wirelessly to the FM receiver, and thus, to the hearing instrument. In particular, FM systems have been standard equipment for children with hearing loss in educational settings for many years. Their merit lies in the fact that a microphone placed a few centimeters from the mouth of a person speaking receives speech at a much higher level than one placed several feet away. This increase in speech level corresponds to an increase in signal-to-noise ratio (SNR) due to the direct wireless connection to the listener's amplification system. The resulting improvements of signal level and SNR in the listener's ear are recognized as the primary benefits of FM radio systems, as hearing-impaired individuals are at a significant disadvantage when processing signals with a poor acoustical SNR.
A typical application of such wireless audio systems is at school, wherein the teacher uses a wireless microphone for transmitting the captured audio signals via the transmission unit to receiver units worn by the students. Since the receiver units and the respective hearing aids are usually owned by the students, the receiver units may be of different types within a class.
Another typical application of wireless audio systems is the case in which the transmission unit is designed as an assistive listening device. In this case, the transmission unit may include a wireless microphone for capturing ambient sound, in particular from a speaker close to the user, and/or a gateway to an external audio device, such as a mobile phone; here the transmission unit usually only serves to supply wireless audio signals to the receiver unit(s) worn by the user.
Examples of analog wireless FM systems particularly suited for school applications are described, for example, in European Patent Application EP 1 863 320 A1 and International Patent Application Publication WO 2008/138365 A1. According to these systems, the wireless link not only serves to transmit audio signals captured by the wireless microphone, but in addition, also serves to transmit control data obtained from analyzing the audio signals in the transmission unit to the receiver unit(s), with such control data being used in the receiver unit to adjust, for example, the gain applied to the received audio signals according to the prevailing ambient noise and the issue of whether the speaker is presently speaking or not.
In applications where the receiver unit is part of or connected to a hearing aid, transmission is usually carried out by using analog FM technology in the 200 MHz frequency band. In recent systems the analog FM transmission technology is replaced by employing digital modulation techniques for audio signal transmission. An example of such a digital system is available from the company Comfort Audio AB, 30105 Halmstad, Sweden under the trademark COMFORT DIGISYSTEM®.
A specific example of an analog wireless FM system particularly suited for school applications is described in International Patent Application Publication WO 2008/074350 A1, wherein the system consists of a plurality of transmission units comprising a microphone and a plurality of analog FM receiver units and wherein only one of the transmission units has an analog audio signal transmitter, while each of the transmission units is provided with a digital transceiver in order to realize an assistive digital link for enabling communication between the transmission units. The assistive digital link also serves to transmit audio signals captured by a transmission unit not having the analog transmitter to the transmission unit having the analog transmitter from where the audio signals are transmitted via the analog FM link to the receiver units.
U.S. Pat. No. 7,778,432 B2 relates to a wireless network for communication of binaural hearing aids with other devices, such as a mobile phone, using slow frequency hopping, wherein each data packet is transmitted in a separate slot of a TDMA frame, with each slot being associated to a different transmission frequency, wherein the hopping sequence is calculated using the ID of the master device, the slot number and the frame number. A link management package (LMP) is sent from the master device to the slave devices in the first slot of each frame. The system may be operated in a broadcast mode. Each receiver is turned on only during the transmission during time slots associated to the respective receiver. The system has two acquisition modes for synchronization, with two different handshake protocols. Eight LMP messages are transmitted in every frame during initial acquisition, and one LMP message is transmitted in every frame once a network is established. Handshake, i.e., bi-directional message exchange, is needed both for initial acquisition and acquisition into the established network. During acquisition, only a reduced number of acquisition channels is used, with the frequency hopping scheme being applied to these acquisition channels. The system operates in the 2.4 GHz ISM band. A similar system is known from U.S. Pat. No. 8,229,146 B2.
International Patent Application Publication WO 2008/135975 A2 relates to a communication network, wherein the receiver wakes up for listening to the preamble of a data packet and goes to sleep again, if no valid preamble is received.
U.S. Patent Application Publication 2007/0086601 A1 relates to a system comprising a transmission unit with a microphone for transmitting a speaker's voice to a plurality of hearing aids via a wireless digital link, which may be unidirectional or bi-directional and which may be used for transmitting both audio data and control data to the hearing aids.
U.S. Pat. No. 7,529,565 B2 relates to a hearing aid comprising a transceiver for communication with an external device, wherein a wireless communication protocol including a transmission protocol, link protocol, extended protocol, data protocol and audio protocol is used. The transmission protocol is adapted to control transceiver operations to provide half duplex communications over a single channel, and the link protocol is adapted to implement a packet transmission process to account for frame collisions on the channel.
European Patent Application EP 1 560 383 A2 relates to a Bluetooth system, wherein the slave device, in a park mode or in a sniff mode, periodically wakes up to listen to transmission from the master and to re-synchronize its clock offset.
U.S. Patent Application Publication 2007/0259629 A1 relates to the transmission of audio signals from a main device, such as a mobile phone, to a peripheral device, such as a headset, in order to establish a wireless personal area network by using an ultra-wide band link, wherein very short pulses of 1 ns or less duration, corresponding to transmission band width of about 500 MHz, are transmitted. In order to reduce power consumption, the transceivers are operated in an interpulse duty cycling mode. In order to better match the peak current consumption from the battery during powered-on times of the interpulse duty cycling to the average current drawn from the battery, a capacitive element is charged when pulses are not being transmitted or received and is then discharged to power the transceiver when pulses are being transmitted or received. It is also mentioned that such system may be used with devices like a microphone and a hearing aid.
In U.S. Pat. No. 5,083,095, which relates to a hearing aid having a microphone preamplifier using a junction field effect transistors (JFET), in order to enhance power supply rejection, it is mentioned that, due to the internal impedance of the power source, in connection with the relatively low power supply voltage, the power output stage may contribute a signal which, due to the high current drawn through the power supply impedance, is equal to or greater than the wanted signal. It is also mentioned that such ripple signals may be reduced by placing a capacitor across the power leads or by placing a large resistor between the power lead and the stage to be isolated, with a capacitor across the normal leads of that stage. It is also mentioned that the drawback of such solutions employing a RC-filter is the relatively large capacitor required therefore.
U.S. Patent Application Publication 2008/0232623 A1 relates to a hearing aid which is recharged via the direct audio input by a battery included in a wireless communication device attached to the hearing aid via the direct audio input, with the transceiver of the communication device likewise being powered by that battery.
U.S. Pat. No. 6,737,838 B2 relates to a DC/DC up/down converter, wherein first a supply voltage is converted to a lower voltage through a step-down DC/DC converter (buck converter) and then, during specific phases of work also the higher voltage is generated from the lower voltage using the same coil in a step-up converter (boost converter) architecture.
Conventional radio receiver units (“boots”) for hearing aids typically use FM-modulation in the VHF frequency band (169 to 220 MHz) and are connected to the hearing aid through a 3-pin plug-in interface having an audio signal pin, a power pin and a common ground pin, wherein the radio receiver boot is powered by the hearing aid battery. The hearing aid typically is provided with a so-called audio shoe, provided by the hearing aid manufacturer, for connection to the standard 3-pin interface. Typically, the batteries of the hearing aid provide for a supply voltage between 1 and 1.5 V, wherein a typical current consumption of, for example, a BTE hearing aid is between 1 and 2 mA. A digital transceiver operating in the 2.4 GHz band typically needs a supply voltage of 1.5 to 3 V and requires a typical current of 25 mA.